The highest point in Oregon, this route gets the vast majority of Hood ascents. A weekday climb during prime season (early May - late June) can avoid most of the crowds.
The South Side is a general term for several different "chutes" on the south side of the mountain, including the Old Chute, Mazama Chute, and Pearly Gates. The most popular route on an given season depends on the snow accumulation and snow conditions.
The Pearly Gates was the most heavily used route to the summit of Mt. Hood until 2006 when a dramatic shift in the Hogsback and the increased steepness of the this route made the Old Chute the more typical ascent route. The left chute of the Pearly Gates offers a short "step" of steeper snow/ice climbing, while the right chute of the Gates can offer several steps of steeper snow/ice. You cross over the bergschrund to get into the Gates. You can descend by rappelling or downclimbing the route, or by traversing over to the Old Chute.
The Old Chute is a great route to ascend if the bergschrund is impassable or Pearly Gates are jammed with people.